Cooling systems generally include an expansion tank having a degas conduit connected to an upper end of a radiator and a return conduit connected to a pump return conduit. It is known that the degas conduit has contradictory requirements, during initial cooling system a large volume of air needs to be transported to the expansion tank but during certain times such as engine warm-up the flow to the expansion tank from the main cooling system needs to be limited in order to speed up heating of the coolant. It is therefore common practice to use a control flow device such as a single orifice restrictor in the degas conduit to minimise these effects.
Such a conventional single orifice restrictor is relatively small (<2 mm diameter) in order to meet these conflicting flow requirements to the expansion tank and so is easily blocked by debris circulating through the cooling system. In addition, the small size of the orifice means that very high velocities are produced through the orifice (>10 m/s) and this combination of high velocity and low pressure tends to exacerbate aeration and cavitation and increase potential erosion of wall material.